Apparatus for treating elastomeric materials

ABSTRACT

Apparatus for adding liquids such as oils to elastomeric materials such as rubber includes a continuous screw press with intermediate chambers where the material is worked under pressure. Liquid is supplied near the center of the chamber through injector bars, and is mixed into the material as it proceeds out of the chamber toward the press exit. The elastomeric materials may be first processed in the press to remove included moisture.

United States Patent Bredeson et al.

[ 51 Feb. 1,1972

[54] APPARATUS FOR TREATING ELASTOMERIC MATERIALS [72] inventors: DeanK. Bredeson; Robert Kent Slaby,

211 Appl. No.: 802,029

[52] US. Cl ..259/109, 100/75, 100/150,

259/9 [51] Int. Cl. ..B01f 7/08 [58] Field of Search ..259/9, 10, 97,109; 100/74,

Q [56] References Cited 2,276,237 3/1942 Lowry ..259/168 X 2,997,9438/1961 Zies ..100/74 3,111,080 11/1963 French et al.... ..100/373,181,454 5/1965 Ginaven et al ..100/74 Primary Examiner-Walter A.Scheel Assistant Examiner-Alan I. Cantor Attorney-Marechal, Biebel,French & Bugg [5 7] ABSTRACT 3 Claims, 5 Drawing Figures UNITED STATESPATENTS 643,891 2/1900 Bussells "loo/121x HEA T 85 EXCHANGER TANK as 92V 90 23 44 45 I i M 000000 43 O O O O 0 O 55 5s 0 5 DR. 40 59 00000 00000000000000000 @OOOOOOOOOOWOOOOOOOOOOOOO BACKGROUND OF THE INVENTION Theinvention has special reference to a system employing a mechanical screwpress for introducing liquids such as plasticizers, extenders, orantioxidants into elastomeric materials such as natural or syntheticrubbers, preferably during a combined drying process of the material. Atypical liquid may be an oil such as a light process oil of thenaphthenic or slightly aromatic type. This oil serves as anintermolecular softener and lubricant which increases the plasticity andworkability of the material so that it can be more easily formed intodifferent shapes. An oil is also frequently used as an extender alongwith carbon black for increasing the bulk of the rubber compound toprovide a lower cost without noticeably reducing any of the significantproperties, and in many cases producing superior properties.

SUMMARY OF THE INVENTION The present invention is directed to improvedapparatus for treating elastomeric materials and the like by compressingthe material in a first stage of a drainage-type screw press to producean increase in pressure and temperature by friction heat for removingthe moisture by drainage and flashing off of the moisture. Apparatus ofthis general type, used for a different purpose and in a different way,is disclosed in US. Pat. No. 3,] I 1,080. The material is worked underpressure while liquid is simultaneously added. The liquid is readilyreceived by the material, and can be worked and pressed into thematerial in the second stage of the press where the pressure may befurther increased. This general overall process when performed in amultistage mechanical screw press not only provides for efficient dryingbut has been found to provide an efficient, thorough and uniform mixingof the fluid into the material. It is especially desirable for use onnatural rubber in which heretofore the mixing of liquids, particularlyoils, has

' presented many difficulties. The continuous process has also beendetermined to be an efficient method of adding oil or other liquids intosynthetic rubber instead of mixing in the liquid during the coagulationstep, which is the present procedure.

Furthermore, by controlling the temperature of the liquid being added,the liquid can be used to provide some cooling effect on the rubbermaterial, in addition to being mixed into it, and thus the addition ofliquid also can perform the added function of controlling thetemperature of the material during the moisture removing process. Bycontrolling and changing the temperature of the liquid, compensation canbe made for possible overheating of the rubber material, and thus aneffective continuous process is obtained where water or moisture isremoved from the rubber material, and oil is added to obtain an oilextended" rubber product. Furthermore, the drying and extendingoperations are all performed in one piece of apparatus and in acontinuous process, where the temperature of the material is maintainedwithin safe limits.

Accordingly, the object of this invention is to provide a novelapparatus for impressing and mixing of a liquid into elastomericmaterials; to provide such apparatus where the addition and mixing ofliquid is combined in one continuous operation with the drying of thematerial; and the liquid may be used to control the temperature of thematerial in apparatus for producing oil-extended dry natural rubbermaterials and the like, wherein the oil is readily pressed and mixedinto natural rubber to assure a thorough dispersion of the oil and ahomogeneous oilextended natural rubber product; and to provide anapparatus wherein liquid can readily be pressed into the elastomericmaterial being treated, at the same time using the addition of theliquid to control the temperature of the material, to avoid overheatingof the material and damage thereto.

Other objects and advantages of this invention will be apparent from thefollowing description, the accompanying drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a somewhat diagrammaticelevational view of a screw press showing one form of the apparatus,with one-half of the cage removed to expose and illustrate themultistage construction, and including a diagram of the circuit forinjecting liquid;

FIG. 2 is an enlarged detail view of one of the injector parts shown inFIG. 1;

FIG. 3 is a sectional view showing details of the valve and injector lugfor adding liquid to materials processed in the apparatus;

FIG. 4 is an enlarged fragmentary sectional view through a portion ofthe cage of the apparatus, illustrating the manner in which openings areprovided between the bars making up the walls of the chamber; and

FIG. 5 is a view similar to FIG. 1 showing a modified form of press.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, whichillustrates preferred embodiments of the invention, FIG. I showssomewhat diagrammatically, a continuous duty, interrupted flight,screw-typeexpressing machine having an inlet hopper 10 through whichmaterials to be worked upon and treated are supplied. The materials arereceived between the flights of the feed screw 12 and carried therebyfrom the hopper 10 into the main body of the apparatus, which is made upof an outer cage structure 15 formed by two symmetrical halves which arebolted together. One-half has been removed in FIG. 1 to illustrate theinterior of the apparatus.

Within this outer cage structure there are a plurality of subassembliesof sections l6, l7, l8, 19, 20, 21, 22 and 23 with sections 16-19forming the first stage of the press and sections 20-23 forming thesecond stage. Each of these sections is formed by a framework supportinga plurality of axially extending screen bars 25 (FIG. 4), in somesections separated by suitable small spacers 26. Further details of theconstruction of these subassemblies are illustrated in US. Pat. No.3,126,820. The important point, as far as the present apparatus isconcerned, is that those sections of the apparatus where liquid is to bedrained are provided with so-called drainage openings defined openingsdefined between adjacent screen bars making up the section, while thesections where injection occurs do not have such openings, at least notnear the point of injection.

Within the elongated cylindrical chamber defined by the casing or cagestructure, and mounted on the main shaft 30, are a plurality of collarmembers 32 some of which may be tapered as shown so as to decrease thecross-sectional area between the collar and the cage section walls.Intermediate these collars, and also fixed to rotate with the shaft, arepressure worms 35. These pressure worms are essentially of likeconstruction, with a worm body 37 and an interrupted flight 38 whichpreferably is notched at a number of locations, as shown in FIG. 2, toproduce a more thorough shearing and working of the material in theapparatus. The main difference between the various pressure worms 35 isthat the worm bodies 37 are of different diameter, progressivelyincreasing generally according to the larger diameter of the precedingcollar. The pressure worms take up material forced around the precedingcollar, and move the material under pressure over and around thesucceeding collar and onto the next pressure worm. Rotation of the shaft30, which produces this action, is obtained from a conventional drive40, which may include any suitable form of power together with a gearcase or the like by which the desired rotation of the feed worm andpressure worms is obtained.

The cage structure 15 preferably is of constant diameter, and has anentrance or feed opening where the feed worm l2 enters the cagestructure, and a discharge opening formed by a discharge ring 42 at theopposite end of the cage structure. This ring preferably is fastened toa rotatable helical gear 43 carried on a threaded extension 44 such thatrotation of the adjusting worm gear 45 will rotate gear 43 and causeaxial adjusting movement of the discharge ring 42.

The collar members 32 and the bodies ofworm members 37 cooperate withthe interior walls of the cage structure to provide a through annularpassage for the material, with such passage varying in cross-sectionalarea at different locations. In one embodiment of the invention thispassage decreases gradually in cross section, so that pressure is builtup on the material in the first stage up to the space around collarmember 50. This collar member includes a portion which may taperinwardly such that the annular space between it and the cage wallsincreases on the downstream side of this collar. Therefore, in thissection and within the following chamber portion 52 surrounding the nextpressure worm, the pressure on the material may be somewhat reduced byreason of the increase in volume permitting expansion of the materialwithin the zone. In this region the spacers are not used, to preventdrainage. Then, progressing toward the discharge end of the cage, thepressure collars may again increase progressively in cross section, andthe worm bodies likewise correspondingly increase in size, such thatpressure is again applied to the material until it reaches the dischargecollar 55 which projects at least partially into the discharge ring 42.Preferably the discharge collar is provided with a set of breaker lugs57 arranged to cooperate with a rotatable shredder member 58 having arotary drive 59. Material passing through the discharge opening isengaged between the shredder 58 and the lugs or teeth 57, and is cut ortorn into relatively small pieces which are expelled through thedischarge ring 42 into any suitable collection device.

One feature of the present invention relates to the relationship of thedrainage or venting opening between the screen bars in the varioussections of the cage structure. As the annular cross-sectional area ofthe passage through the apparatus decreases, the pressure on thematerial will increase. It is understood that in operation the passagebetween the rotatable parts and the walls of the cage structure isessentially full of compacted material which is being continuouslyworked and compressed. This results in substantial frictional heating.If desired, this heating may be regulated by flowing heat exchange fluidor liquid through suitable passages such as shown in said U.S. Pat. No.3,126,820. As pressure on the material increases, the tendency is tosqueeze some of the material into the drainage openings between screenbars 25, therefore it is desirable to attain a balance between themaximum size of opening for the best possible drainage and suchreduction in the opening as mentioned above to avoid complete cloggingthereof by materials squeezed into the openings. Where pressure on thematerial is first released, as in chamber portion 52 at the end of thefirst stage, the drainage opening size is increased, thereby assuringthe best possible venting and removal of vapors and liquids. By way ofexample, in one form of apparatus constructed in accordance with theinvention the drainage opening between screen bars 25, in the section16, is approximately 0.060 inch in width. Comparable openings in section17 are reduced to 0.040 inch, in section 18 the openings are reduced to0.030 inch, and in the first part of section 19 the drainage openingsare further reduced to 0.020 inch in width. In the last part of section19 the opening size is increased to about 0.060 inch, then there are noopenings in section 20. The size ofdrainage openings in sections 21, 22and 23 decreases in size corresponding to the sizes for sections 17, 18and 19. It has been found through operation of apparatus of this typethat vapors tend to flow to the point of lowest pressure, in other wordsto the entrance to chamber portion 52, around collar 50 and by havinglarger drainage openings at this point it is possible to achieve optimumventing, thereby assuring that all vapors are quickly removed from thechamber.

As shown in FIG. 1, stationary breaker lugs, indicated by the generalnumeral 60, are provided to prevent rotation of the material with thecollars 32 and to cooperate with the notched worm flights 38 to obtain atearing, shearing and working action of the material. However, a featureof the invention is provided by the specific construction of the breakerlug 62 (FIG. 3). The breaker lug 62 is spaced outward from the collarwithin the chamber portion 52. A controlled injection nozzle 63 (FIG. 2)is mounted in lug 62 for directing plasticizing oil into the middle ofthe mass of material in this chamber portion.

Details of one nozzle are shown in FIG. 3. The tubular body 65 is fittedinto the lug, and a valve stem 66 carries a head 68 which cooperateswith a seat 69 to control flow into the chamber. The stem has a threadedpart 70 which is received in a piston 71 movable in a cylinder 72. Oilunder pressure is supplied to the stem side chamber 73 when it is to beinjected. This automatically opens the nozzle. Valving the oil underpressure to the opposite chamber 74 will shut off the nozzle. Theprojecting stem 75 provides a means for locking the nozzle closed ifdesired, and also gives a visual indication of nozzle position.

The liquid plasticizer to be mixed with the rubber material is suppliedfrom a pipe or manifold which may receive this fluid from a positivedisplacement reciprocating cylinder pump 82. Particularly in thetreatment of natural rubber and the like, a liquid such as oil is usedto provide a so-called oil extended" rubber product. This oil isprovided from a suitable tank connected through pipe 86 to aconventional heat exchanger 88 which is employed to heat the oil to adesired temperature. The oil thus is maintained at a predeterminedtemperature, which can be controlled by suitable control of the heatingexchanger 88. This temperature of the oil preferably is somewhat lessthan the temperature of the material encountered in the chamber portion52 of the press, such that the oil tends to absorb some heat from thefrictionally heated rubber material and thereby provide a cooling effecton the rubber which prevents overheating and damaging of the rubbermaterial. At the same time, the warmed oil is thoroughly mixed into therubber material by reason of the mechanical working of the material fromthe notched pressure worm flights and the interaction of these flightswith the collars and breaker bars. A bypass 90 is provided around theheat exchanger 88, and a control valve 92 is included in the bypass,whereby cool oil from the tank can be supplied directly to the cylinder82 ifadditional cooling effect should be needed.

The cylinder 82, as shown in FIG. 1, is of the reciprocatingdouble-acting type, which receives the oil to be injected through thecheck valves 95 and delivers the oil through check valves 96 into amanifold 97 which leads to the entrance tubes 75 of the injectors. Apressure-relief valve 98 is provided, which will bypass oil back to thetank 85 if the pressure increases beyond a predetermined limit. Thisarrangement provides positive displacement pumping at relatively highpressure, to assure that the oil is effectively injected into thematerial within the press.

The pump 82 is driven by a double-acting reciprocating motor 100 whichis connected to the pump through a coupling 101. A separate hydrauliccircuit for driving the motor 100 includes a tank T2 from whichhydraulic fluid is pumped through pump 103 to a conventionalservo-operated reversing valve 105. This valve has pilot cylinders 106at its opposite ends connected to the opposite heads of the motor 100,thus as the motor piston reaches one limit of its stroke, the buildup ofpressure will cause the appropriate pilot 106 to shift the valve therebyreversing the pressure connections to the motor 100 and reversing itsdirection. At the same time the return connection to tank T2 is likewisereversed. An adjustable bypass valve 108 is connected to the outlet sideof pump 103, and by adjusting the pressure of the pump outlet side ofpump through this valve, it is possible to increase or decrease thereciprocating speed of the motor 100, thereby controlling the rate ofdisplacement of the pump 82.

FIG. 5 illustrates a modified form of apparatus which may be used inaccordance with the invention. The press structure is generally of thetype disclosed in greater detail in copending application Ser. No.763,647, filed Aug. 19, 1968 entitled MECHANICAL SCREW PRESS, now U.S.Pat. No. 3,574,891 issued Apr. 13, 1971 which is assigned to theassignee of this application. Apparatus of the type shown in FIG. 5 hasbeen found particularly advantageous in drying of natural rubber. Itdiffers from the apparatus shown in FIG. 1 primarily in two respects.There is an intermediate choke ring 110 in the chamber of the press,upstream from the injector nozzle 112, which extends through bar 114,and which is of the same construction as shown in FIG. 3, and previouslydescribed. Secondly, in place of the shredder structure shown in FIG. 1,an extruder section 115 is provided at the discharge end of the press,including an imperforate extruder barrel 116 which is of smallerdiameter than the intermediate diameter of the press chamber, and adouble helical extruder worm 118 operates within the barrel 116. At thedischarge of the barrel 116 there is a die plate 120 through which therubber material is discharged, and a rotating knife 122, driven from aseparate motor (not shown) cuts the material extruded through the dieinto relatively small particles. In this apparatus, the rubber materialis essentially free of moisture, while adding to it the oil injectedthrough the nozzle 112.

By use of the above-described screw press apparatus, the addition ofliquids to rubber material is accomplished easily and completely in thesame operation by which moisture is removed from the material. This isparticularly advantageous in the treating and handling of natural rubbermaterials, where addition of liquids has heretofore required rathercomplex operations. Furthermore, the liquid besides being thoroughlymixed into the final product may also assist in controlling thetemperature of the rubber material, and thus prevents overheating anddamaging ofthe rubber material.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of ap-' paratus, and that changesmay be made therein without departing from the scope of the invention.

What is claimed is:

1. An improved screw press apparatus for continuous drying ofelastomeric material and for mixing of fluid into the material duringthe drying operation, comprising wall means defining an elongatedchamber having drainage openings therein, conveying and working meansincluding a shaft rotatably mounted within said chamber and adapted tobe power driven and a plurality of successive collars and worm bodieshaving flights thereon and mounted on said shaft with at least said wormbodies connected for rotation with said shaft, stationary breaker lugsextending between said worm flights for cooperating with said flights toprovide a shearing and working action on the material, and said chamberbeing divided into at least first and second stages in each of whichsaid working and conveying means increases progressively the pressure onthe material conveyed through the chamber, means forming a zone betweensaid stages in which pressure on the material is effectively decreased;the improvement comprismg,

the drainage openings in said first stage being progressively reduced insize corresponding to the increase in the diameter of the working andconveying means to minimize extrusion of the material through saidopenings as the pressure increases while providing for escape ofmoisture and vapor released from the material,

said drainage openings being of increased size in said zone betweenstages to provide optimum venting from said zone,

said wall means being imperforate immediately downstream of saidexpansion zone, and means for injecting a liquid into the regionsurrounded by imperforate wall means for mixing of the liquid into thematerial within the second stage.

2. Apparatus as defined in claim 1, wherein said injecting meansincludes an injector nozzle extending through one of said breaker lugsto release the liquid near the center of the chamber.

3. Apparatus as defined in claim 2, including a positive variabledisplacement pump means adjustable independently of the press speed andconnected to deliver the liquid under pressure to said nozzle.

1. An improved screw press apparatus for continuous drying ofelastomeric material and for mixing of fluid into the material duringthe drying operation, comprising wall means defining an elongatedchamber having drainage openings therein, conveying and working meansincluding a shaft rotatably mounted within said chamber and adapted tobe power driven and a plurality of successive collars and worm bodieshaving flights thereon and mounted on said shaft with at least said wormbodies connected for rotation with said shaft, stationary breaker lugsextending between said worm flights for cooperating with said flights toprovide a shearing and working action on the material, and said chamberbeing divided into at least first and second stages in each of whichsaid working and conveying means increases progressively the pressure onthe material conveyed through the chamber, means forming a zone betweensaid stages in which pressure on the material is effectively decreased;the improvement comprising, the drainage openings in said first stagebeing progressively reduced in size corresponding to the increase in thediameter of the working and conveying means to minimize extrusion of thematerial through said openings as the pressure increases while providingfor escape of moisture and vapor released from the material, saiddrainage openings being of increased size in said zone between stages toprovide optimum venting from said zone, said wall means beingimperforate immediately downstream of said expansion zone, and means forinjecting a liquid into the region surrounded by imperforate wall meansfor mixing of the liquid into the material within the second stage. 2.Apparatus as defined in claim 1, wherein said injecting means includesan injector nozzle extending through one of said breaker lugs to releasethe liquid near the center of the chamber.
 3. Apparatus as defined inclaim 2, including a positive variable displacement pump meansadjustable independently of the press speed and connected to deliver theliquid under pressure to said nozzle.